1. Technical Field
The present disclosure relates to an ignition coil with ionization and digital feedback for control and diagnostics in an internal combustion engine.
2. Background Art
Manufacturers continue to improve control of internal combustion engines to enhance fuel economy and performance while reducing emissions using more sophisticated sensing and processing hardware and software. Ionization signal sensing (or ion sense) uses a bias voltage applied across a sensor positioned within the combustion chamber to generate a signal indicative of combustion quality and timing. Previous engine control strategies have used this signal to monitor or control the combustion process. The ionization signal is typically ignored or masked during spark discharge with the ionization waveform occurring after the spark discharge but during combustion analyzed for control and diagnostics, such as described in U.S. Pat. No. 6,865,929, for example. For spark-ignition engines, one or more spark plugs may be used as an ion sensor after the spark is generated to initiate combustion by applying a bias voltage across the air gap of the spark plug, or between a spark plug electrode and the cylinder wall.
Spark-ignited internal combustion engines may be configured with ignition systems that feature two or more spark plugs for each cylinder to accommodate flexible fuel applications, or to provide more ignition energy for leaner air/fuel ratios to improve combustion and enhance fuel economy, for example. Multiple spark plugs may be powered from a common ignition coil to improve cost effectiveness of these applications. However, multi-plug applications powered by a common ignition coil present various challenges for implementing ion sensing technology and ignition coil control and diagnostics. Likewise, single plug-per-cylinder applications that use a multiplexed or wired-OR arrangement having a single ignition control line for more than one cylinder present challenges for ion sensing and ignition coil control and diagnostics. For example, combining or summing feedback or ionization current signals from two or more spark plugs or other ion sensors on a common signal line may result in attenuation or cancellation of high frequency components and associated variation in the ion sensing signal that is difficult to correlate with actual combustion performance. Differences in spark durations between two or more spark plugs can mask ion signals for a portion of the engine cycle so that combustion information is unavailable. In addition, electrical and magnetic coupling of the spark discharge can also distort the ion sense signal. Systems and methods for addressing these issues using an isolation device are disclosed in commonly owned and copending U.S. patent application Ser. No. 11/929,949, the disclosure of which is incorporated by reference in its entirety. While suitable for many applications, systems and methods disclosed herein provide additional advantages relative to various prior art strategies.